1. Field of the Invention
The present invention relates to an electrical connector, and more particularly to a high density land grid array connector for connecting an integrated circuit package to a printed circuit board, having space efficient contacts which facilitate the signal transmission between the connected components.
2. The Prior Art
The use of high density integrated circuit (IC) packages of the LSI/VLSI categories is becoming increasingly more common as the trend of the computer market continues toward compactness requiring the miniaturization of IC packages. Input/output pins of such IC packages to be mounted on a printed circuit board (PCB) are arranged in such a dense pattern (sometimes as many as two hundred closely spaced contact elements) that direct soldering of the IC package to the PCB creates several significant problems in inspecting and correcting any resulting soldering faults thereof. Therefore, a socket having a plurality of conductive contacts is commonly employed for engaging the pins of the IC package and providing an electrical path to the PCB.
A pin grid array (PGA) type IC has a number of lead pins projecting downwardly from a lower surface of the main body thereof. The pins are matingly received in corresponding contacts of a related PGA socket which are engaged with holes defined in predetermined locations on the PCB for connecting with electrical circuitry thereof. PGAs along with their associated sockets and contact elements are disclosed in U.S. Pat. Nos. 4,381,130, 4,498,725, 4,648,669, 4,674,811, and 5,057,031.
One shortcoming of the PGA type IC is the tendency of the pins thereof to become easily damaged. Therefore, a ball grid array (BGA) type IC has been introduced which has essentially the same structure as the PGA except that ball-shaped contacts replace the conventional straight pins of the PGA thereby effectively overcoming the pin damage drawback. Such BGAs have previously been disclosed in U.S. Pat. Nos. 5,518,410, 5,547,389, and 5,641,297.
Unfortunately, the small engagement surface area of the ball-shaped contacts do not provide an adequate electrical connection with the contacts of the corresponding socket. In addition, both PGAs and BGAs are ineffective in applications requiring a denser-than-usual contact element arrangement, such as for a central processing unit (CPU) used in portable computers. Such high density contact elements would result in closely positioned holes in the PCB for engagement therewith which becomes laborious due to spatial constrictions.
To overcome the limitations of the PGAs and BGAs in the case of very dense contact elements, a land grid array (LGA) type IC has been introduced. The distinctive characteristics of the LGA socket are embodied in the resilient contact elements which each expose portions thereof to both the upper and lower surfaces of the socket for engaging with flat contact pads located on a bottom surface of the main body of the IC package and on a top surface of the PCB, respectively. The contact elements of the LGA socket are formed having two free ends which are spaced apart a predetermined distance in the unassembled state. When the IC package is assembled with the LGA socket and mounted on the PCB, a normal force causes the two free ends of each contact to contact each other thereby shortening the signal transmission path therethrough. If the free ends do not contact each other due to an insufficient normal force, the signal will still be transmitted through the contact but along a longer path. U.S. Pat. Nos. 4,684,184, 5,199,889, and 5,232,372 disclose prior art LGAs.
The contact elements associated with the prior art LGAs exhibit different shapes but the basic component of each lies in the two free ends being connected by a curved portion which provides the contact with resiliency so that the two free ends will touch when the IC package is assembled with the socket and mounted on the PCB. Due to the extended length of the curved portion, the LGA socket must have a substantial thickness to enclose the contacts in passageways therein which increases the space occupied by the LGA assembly. Furthermore, the prior art LGAs do not address factors which may result in signal loss such as PCB warpage or oxidation formed on the contact pads of the IC package. Therefore, an improved contact for use in an LGA socket is required which can overcome the drawbacks of conventional LGA socket contacts.